This invention relates to a sliding bearing for a light alloy housing used in an internal combustion engine of an automobile or the like which bearing comprises a back metal layer of a copper alloy and an aluminum alloy bearing layer.
There are already known various kinds of sliding bearings. Generally, an aluminum alloy sliding bearing comprises a bearing layer of Al--Sn alloy, Al--Pb alloy, Al--Zn alloy or the like formed on a back metal of JIS 3141SPCC, SAE1010 or the like. Most of the back metals used in such a sliding bearing are made of low-carbon steel whose carbon content is usually not more than 0.20%.
A housing for such a bearing is made of cast steel, cast iron, carbon steel or alloyed steel, and is analogous in thermal expansion coefficient to the back metal of the bearing, and therefore even when the temperature rises during an operation, the bearing and the housing are kept in intimate contact with each other with no gap developing therebetween, thus posing no particular problem.
With respect to the characteristics of the conventional sliding bearings, attention has been directed mainly to the properties of the alloy bearing layer, and as regards the back metal, its workability and bonding property have drawn attention.
Recently, however, in view of an energy-saving design and a lightweight design of an internal combustion engine of an automobile, there is an increasing tendency that an aluminum alloy is used to form an engine block, a connecting rod and so on.
Where the housing for the bearing is thus made of an aluminum alloy, the bearing having the conventional back metal of steel is greatly different in thermal expansion coefficient from the housing, and therefore the close contact between the bearing and the housing fails to be maintained at elevated temperatures, so that damage such as fatigue and seizure due to fretting (which means a surface damage developing when a slight relative motion is periodically repeated between two contact surfaces) or migration (which means a phenomenon that Cu-plating, flash-plating and carbide of oil concentrate locally as a result of a periodic relative motion) develops. On the other hand, there has been another problem that damage such as seizure has occurred very frequently under severe conditions of use, as at a high engine speed obtained as a result of a high-performance design of the engine.
An attempt has been made to increase an interference so as to improve the condition of close contact of the bearing with the housing at high temperatures or under a high load; however, the bearing having the conventional back metal of low-carbon steel is low in strength, and when attaching the bearing with a high assembling stress, it deforms beyond its elastic limit to be buckled. Besides, such a bearing has a low heat transfer coefficient, and is inferior in heat dissipation, and therefore is not entirely satisfactory in seizure resistance.